You can trade any Index successfully by only looking at that chart. However if you are looking for an edge you might want to look at the market as a whole.

Supple & Demand moves the market, and my take on that is emotion makes the decision. But it depends on your timeframe as to whether you gain any edge from looking at other indicies. You need to be trading very small timeframes.

There are several advantages to running multiple indicies together on small timeframes.

1. This depends on your technique, but one market will react perfectly on a S&R while the ES is a little off. You will see how the emotion in one market moves before the ES and why the ES didn't react perfectly on it's S&R.

2. The markets can look very different to eah other, but at a closer look most up and down reactions occur at almost the same time - only different speeds and amplitudes make them look different. It's the perfect set up on one that gives the edge to trading another. Again, to gain the advantage you need to be in the lowest timeframes.

3. Don't underestimate the cash market - it leads at times - showing the perfect S&R. Try looking at the Dow on a 200Range chart and you'll see what I mean.

But if you can't make the ES work on its own then this only complicates and slows you down. If you're making it and you're nimble, this will give you an edge.

You've got to watch ES, NQ, YM, and ER2. ER2 is the main contract used to arb. You can sometimes see the spread traders leaning on the ER2 to get long NQ's or ES. Or the opposite. The interplay between the different market centers gives you the overall feel for what the big money is trying to hide. Remember, if you had 100 million dollars of stock you want to buy, you would not just buy it, you would push the futures down so you can get a good price.